The objectives of this research program are elucidate the central neural mechanisms which participate in the production and regulation of circadian rhythms. Our objectives for the current year are to analyze the organization of the suprachiasmatic nucleus by Golgi analysis, ultrastructure and immunohistochemistry. In addition, we shall further analyze the effects of neonatal suprachiasmatic nucleus lesions on circadian rhythmicity and will study the effects of differential ablation of output of the nucleus on the development of circadian rhythmicity.